The present invention relates to a tension adjusting mechanism for applying a predetermined tension to a wire, for example, used for a wire saw.
In the case of cutting a work made of a hard and brittle material such as a semiconductor material, a magnetic material and a ceramic, a wire saw has been used. In the wire saw, a plurality of working rollers are provided at a predetermined interval, and a plurality of annular grooves are formed on an outer periphery of each of the rollers at a predetermined pitch. Further, between the working rollers, a wire is successively wound around the annular groove, and a predetermined tension is applied to the wire by means of a tension adjusting mechanism. Then, a slurry containing float abrasive grains is supplied to a portion on the wire while the wire is moved, and the work is pressed to and brought into contact with the wire in this state, so that the cutting process is given to the work.
In accordance with the tension adjusting mechanism in this kind of wire saw of the conventional art, as shown in FIG. 11, a dancer roller 52 is rotatably supported to a front end of a rotatable dancer arm 51 mounting a weight W thereto in an adjustable manner, and the weight W is directly provided in the dancer roller 52 so as to apply a tension to a wire 54. Two guide rollers 53 are disposed in such a manner as to oppose to the dancer roller 52, and a wire 54 is wound on the dancer roller 52 through these guide rollers 53. The weight W is mounted to the front end of the dancer arm 51, and the dancer roller 52 is rotated and urged to a direction of being apart from the guide roller 53 by the weight W, so that it is structured such that a predetermined tension is applied to the wire 54.
However, in the conventional tension adjusting mechanism, the wire 54 is guided to the portion on one dancer roller 52 through the guide roller 53. Accordingly, when the wire 54 is tensed or loosened in correspondence to a sudden speed increase and decrease of the wire 54, the dancer roller 52 is vertically oscillated (hunted) at a great amplitude corresponding to half of a tensioning amount or a loosening amount of the wire 54 so as to maintain a predetermined wire tension. Then, there have been problems that the great oscillation is transmitted to the guide roller 53 and a working roller (not shown) through the wire 54 so as to abrade the rollers at an early time, and the oscillation is transmitted to the working roller so that a working accuracy is lowered. Further, in the case that the oscillation is sudden, there has been a case that the wire 54 is cut.